Froth flotation of silica from iron ore



Patented May 6, 1 947 FROTH FLOTATION 0F SILICA FROM IRON ORE Julius Bruce Clemmer and Milton Friel Williams, In, Tuscaloosa, Ala.

No Drawing. Application December 11, 1944,

- Serial No. 567,762

6 Claims. '(Cl. 209-166) (Granted under the act at March 3, 1883, as

The invention described herein may be manufactured and used by or for the Government. of the United States for governmental purposes without the payment to use of any royalty thereon in accordance with the provision of the act of April 30, 1928 (Ch. 460, 45 Stat. L. 467).

This invention relates to an improved process for beneflciating iron ores whereby froth flotation of the siliceous gangue constituents yields an iron enriched product; more particularly it relates to a froth flotation process for siliceous gangue constituents in iron ores employing anionic collecting agents in deslimed iron ore pulps substantially saturated with hydrated lime.

An object of this invention is to provide a froth flotation process for beneflciating iron oxides in pulps containing them in the presence of siliceous gangue. A further object is to provide a flotation process for separating silica from iron oxides employing anionic collection agents. A still further.

object is to provide a flotation process forbeneflciating iron ores or products containing both calcareous and siliceous materials. Still other objects include the development of a flotation process which will have greater selectivity in separating siliceous materials from iron ores and thereby efiect greater operating economies. Other objects, purposes, and advantages of the invention will hereinafter more fully appear or will be understood from the detailed description of its practice. i

We are aware that various methods have been proposed for beneflciating iron ores by flotation methods for the purpose of recovering an iron enriched product by rejecting siliceous gangue constituents. The most common flotation method known to the art is the flotation of the iron oxides from the siliceous angue constituents, employing an anionic collecting a ent. such as oleic acid or sodium oleate, in conjunction with auxiliary reagents, such as soda ash or sodium silicate, to retard flotation of the silica. Those skilled in the art recognize that soa flotation of the iron oxides has limitations. The method yields good resuits on some iron ores, but is not applicable to others. The fine oxides are reluctant to float with moderate quantities of collector, and the voluminous froths are diflicult to handle. Desliming of the ore pulp is often necessary before good flotation 01' the granular ox des can be achieved, and the pulps must be relatively free of soluble salts. The salts, such as lime or magnesia. derived from the ore or present in the water em loyed, activate the siliceous gangue to flotation with the soap collecting agents and invariably results in poor selectivity. A soft water relatively free of lime and magnesia is necessary for satisfactory soap flotation of iron oxides.

An alternative method for beneficiating iron ores by flotation has been to reverse the separaamended April 30, 1928; 370 0. G. 757) 2 tion and float the siliceous gangue minerals from the iron oxide by employing cationic collecting agents. The application of cationic collectors to tors.

phosphate.

iron ores has been described by Kirby and Gillson in United States Patents Nos. 2,217,684 and 2,221,485. This method of flotation is attractive in that iron ores in general contain less siliceous material than iron oxides, and flotation of the silica is in keeping with the preference of those skilled in the art for floating that constituent which occurs in least amount. The cationic collecting agents are not without their limitations. They are, in general, more expensive than those of the anionic type. Moreover, the are not particularly selective, nor are they effective silica col-,- lectors in the presence of slime. Cationic collectors exhibit a pronounced tendency to float fine iron oxides and slime gangue constituents without discrimination in voluminous froths which are exceedingly difiicult to handle. Those skilled in the art recognize that the inability tofloat granular siliceous materials from slime-bearing iron ore pulps is an inherent limitation of cationic collec- Prior desliming of the pulp or an initial frothing operation to reject the slime is often obligatory for satisfactory cationic flotation of granular siliceous materials from ironoxides.

In a co-pending application, assigned to thesame assignee as the present application, by Julius Bruce Clemmer andBallard H. Clemmons, Serial No. 473,162, filed Jan. 22, 1943, is described a process for beneflciating iron ores by froth flotation of the siliceous gangue' constituents from the iron oxides to recover an iron enriched I product. Briefly, the method consists of froth flotation of activated siliceous gangue constituents from iron oxides employing anionic collecting agents, such as the fatty acids, rosin acids, or their derived soaps, in caustic alkaline pulps with a pH of at least 10, while retarding flotation of the iron oxides with a metaphosphate or poly- The flotation process is particular- 1y well adapted for beneflclating calcareous iron ores containing calcite, limestone, dolomite, etc., associated with siliceous gangue materials, such as quartz, as exemplified by the calcareous red ores of the Birmingham district, Alabama. The quarts and granular silicates in such .ores are, in general, naturally activated to soap flotation, presumedly due to lime or magnesia salts in the ore. The calcareous iron ore pulps are invariably alkaline and qualitative tests on the water shows presence of lime or magnesia salts which actior rosin. field collecting'agent. Desliming of the also applicable to siliceous iron ores relatively free of calcareous materials. These ores, exemplifled by the weathered red ores of the Birmingham district and the siliceous ores of the Lake Superior district, being relatively free of lime or magnesia salts, contain non-activated siliceous gangue constituents. The silica in such ores can be activated to soap flotation by addition of a metal salt. Conditioning a caustic-alkalinepulp of the ore with-a moderate quantity of certain metal salts, such as the soluble salts of. calcium magnesium, strontium, barium, or lead, suiflces to activate the silica to flotation by the as rosin acid collecting agents without adverselyef11.-

fecting retardation of the iron oxides ';by:=,the: phosphate depressants. Hydrated limemayi'alsolfj activator, care must be exercised to'avoid fr lime salts in the flotation pulp as they materially increase the phosphate requirements. Grinding or blunging the ore with suflicient hydrated ime complete activation of the silica. The free lime I ;'-vention are subject to considerable variation, and

to establish a pulp pH of about 11 insures rather- I be employed to activate the silica to flotatiomand from the standpoint of cost is particularly ate tractive. When using hydrated limeas the silica salts in the lime conditioned pulp may be 'removed by washing with fresh water or addition-- of soda ash to the pulp to precipitatethe lime as carbonate. tion of the silica from the phosphate retarded iron oxides.

This enables subsequent soap flota such as clay, are objectionable in that they are reluctant to float with the granular silica and when present in appreciable amount yield contaminated iron products. Some oxide or gangue slime is permissible, however, and completely deslimed pulps need not be employed in the practice of this invention. A -pulp substantially ireeof slime is suflicient and permits acceptable flotation of the silica with moderate quantities of collector to yield an iron enriched product of the desired grade.

The anionic collecting agents which we have found suitable for flotation of the siliceous gangue from iron oxides in the practice of this invention include oleic acid, red oil (crude oleic acid), purified and crude sodium oleate, flsh oil fatty acid, flsh oil soap, sodium resinate, mixtures of impure rosir and fatty acids derived from tallol recovered from sulfate paper mill black liquors, purified or crude sulfate soap (skimmlngs from sulfate paper mill black liquors) and various crude or purified tallols. .The

tallols and sulfate soaps recovered from paper mill black liquors are relatively inexpensive and were the preferred collectors.

The lime used in the practice of this invention to retard the iron oxides and activate the sillceous materials to flotation may be added to the flotation pulp as either quick lime (CaO) or hydrated lime (Ca(OH) 21 in dry powdered form, or as; a. slurry of hydrated lime. Addition of the 1- lime as a slurry insures thorough mixing with the pulp for maximum effectiveness, and is preferred.

The proportion of hydrated lime and collecting, agents employed in the practice of this inexperimentation for any particular case. Froth characteristics and purity of the separated prod- 'ucts serve as reliable guides for reagent adjustment. An excess of collecting agent promotes .flotation of a portion of the iron oxides with the As a result of extended research and experimentation, we have discovered animproved method of beneficiating iron ores by froth flotation of the siliceous gangue constituents employtivating the silica to soap flotation and' 'retardingri flotation of the iron oxides. Sufllcient hydrated.

lime to saturate the deslimed pulp adequately re tards the iron oxides, and other iron depressants, such as the metaphosphates or polyphosphates, need not be employed in the practice of this invention. Addition of a moderate quantity of an anionic collecting agent, such as a" fatty acid, rosin acid, or their derived soaps, to a deslimed iron ore pulp saturated with lime enables rapid and essentially complete flotation of the siliceous gangue to yield an iron enriched product.

A prime requisite in the practice of this invention is that the iron ore pulp be relatively free of slime. Both iron oxide and gangue slimes in the nounced tendency to float with the activated siliceous materials on adding a soap collecting agent and result in the formation of voluminous froths which are diflicult to handle In addition to incurring an unavoidable loss of fine iron in the silica product; the iron slime consumes collector and increases the quantities needed to float the Slime tranlme constituents.

sill man: In nfp'ri a] out adversely affecting the separation. quantity of lime needed to retard the iron oxides during silica flotation varies for different ores,

silica wherea a deficiency of collector results in incomplete flotation of the silica.

Control of the collector is not critical and moderate variation in quantities employed is permissible with- The depending upon their lime consuming capacity. Iron ores containing soluble acidic salts require more lime than ores free of such salts. The calcareous iron ores which yield pulps containing soluble calcium salts generally require less lime than the siliceous ores. The optimum quantity of lime for retarding the iron oxides during silica flotation can best be determined by trial. In the practice 01' our invention, it is desirable that sufiicient lime be employed to establish a pulp pH exceeding'll, and preferably 12, to insure retardation of the iron oxides. A pulp partly saturated with lime suffices on many ores, but best results are obtained with pulps substantially saturated with lime. Lime in excess of saturation requirementis not deleterious, but should be avoided to minimize waste of reagent. A deflciency of lime, as evidenced by a pulp pH of less than 11, is objectionable, however, as part of the iron oxides may float with the silica due to incomplete retardation.

It will be apparent to those skilled in the art ods. The flneness of grind may vary from 35 to 200 mesh or finer, depending on the degree of liberation of the particular ore; substantially complete liberation of the iron oxides and siliceous gangue is essential for a satisfactory separation by flotation-and the fineness of grind should be selected accordingly. The comminuted pulp is deslimed by conventional classification or sedimentation methods to yield a. granular product for flotation substantially free of slime. The ground and deslimed pulp is then subjected to froth flotation to reject the siliceous gangue materials and recover the iron oxides in the following manner. The pulped material is conditioned with sufflcient lime to substantially saturate the pulp as evidenced by a pH exceeding 11, and preferably about 12. A desired quantity of a fatty or rosin acid collecting agent is then added, and the pulp froth floated by customary mechanical or pneumatic methods to yield a rougher froth product enriched in siliceous gangue materials and a pulp residue enriched in iron oxides.

The froth product may contain some iron oxides which floated with the siliceous materials in the roughing operation, and may be repulped with additional water and re-floated to recover these iron values. One or more of such cleaning steps sumces to yield-a final silica reject product of low iron content. Additional lime may be used in the cleaning operations to facilitate retardation of the iron oxides, and additional collecting agent may also be added, if desired, to expedite more rapid and complete flotation of the silica. The iron enriched middlings from the cleaning steps may be combined with the pulp residue from the initial roughing operation, or returned to the preceding flotation step or other convenient points in the flotation or grinding circuit for retreatment as desired.

Conventional flotation terminology designates the floated product from roughing and.cleaning operations as concentrates, and the pulp residues versed and the gangue is floated from the eco-v nomic mineral, the terminology may become confused. To avoid possible confusion in describing the results of our tests, we shall hereafter designate the iron enriched pulps from the roughing and cleaning steps as iron concentrates, rougher and "iron concentrates, cleaner, respectively. The floated silica products from the roughing and cleaning steps will be designated as "rougher froth and silica rejects, respectively.

In the practice of our invention, we prefer to condition the deslimed pulp with lime before addition of the collecting agent. A moderate conditioning sufiices to activate the silica to subsequent flotation with minimum collector and adequately retards the iron oxides. Prolonged conditioning of the pulp with lime is not objectionable, but should be avoided because the attritioning action of particles in the pulp may degradate the softer iron oxides and increase the quantity of slime. The lime may be added to 6 the grinding step if desired, although desliming' may become somewhat more dimcult.

The invention will be further illustrated, but is not intended to belimited by the following examples of practice? Example I I v A sample'of calcareous red iron ore was obtained from an operating mine in the Birming The' ore was typica of ham district, Alabama. the district and containedhematite associated with a. gangue composed predominately of quartz and calcite with minor amounts of 1 accessory calcareous and siliceous materials including shale and ferruginous clay. A head analysis gave 36.6

percent Fe, 12.9 percent CaO, and 21.4 percent hydrochloric acid insoluble (hereinafter referred tap water in a laboratory rod mill. The ground charge was diluted to a volume oi-2.5 liters with additional tap water to g'ive'a pulp containing" about 10 percent solids.- The pulp wasthen dispersed using the equivalent of one pound of l I caustic sode per ton of ore and 04 pound per ton of sodium meta silicate. The-dispersed charge 1 was fractionated by sedimentation and decanta-f 'z" tion to remove the bulk of the slime finer than 20 microns. The granular portion, essentially free of slime and coarser than 20 microns, was repulps-d with additional tap water and transferred to a. small mechanical flotation cell of standard design. 'Sunicient tap water was added to give a slurry containing about 20 percent solids for fiotation. The pulp was conditioned for 2.5 minutes I with the equivalent of 10.6 pounds of hydrated lime per ton of flotation feed which yielded a pulp pH of 12.2. A crude sulfate soap recovered as skirnmings from paper mill black liquors was chosen as the collector for the test, and a quan tity equivalent to 1.3 pounds per ton of flotation feed was added to the pulp substantially saturated with lime. The pulp was conditioned with the collector about one minute, and air was then allowed to enter the cell and resulted in the immediate formation of a silica enriched froth. The froth was collected for 2.5 minutes when flotation of the silica was complete. The rougher froth was cleaned by re-pulping with additional tap 7 W i ht Assay, Percent g gggf eg Product Pel'bcut Fe 050 Insol. Fe CBO Insol.

Iron Concenates Rougher 56.6 47.7 8.9 11.1 30.7 5 37.3 26.6 Cleaner 4.4 38.4 11.3 20.4 5.1 3.7 3.8

C o m 1 Z i posite. 61.0 47.0 0.1 11.8 85.5 41.0 30.4 Silica Rejects. 39.0 12.2 1 20.4 42.2 14.2 50.0 69.6

C o m posite j Fecd 100.0 33.4 13.5 23.6 100.0 100.0 100.0

. insoluble.

The flotation silica rejects which accounted for 39.0 percent of the weight of the feed contained 69.6 percent of the insoluble in the feed and only 14.2 percent of the iron. The iron concentrates from the cleaning step (middlings) were sufllciently high in iron and low in insoluble to be considered fl..ished grade. The combined composite iron concentrates from the roughing and cleaning operations represented a recovery of- 85.8 percent of the iron in a product containing 47.0 percent Fe, 9.1 percent CaO, and 11.8 percent Flotation of the silica. improved the iron content 13.6 percent and decreased the lime and insoluble contents 4.4 and 11.8 percent, re-

spectively.

It will be noted that part of the calcite in the flotation feed was floated with the silica in the recorded test. Flotation tests on a variety of calcareous iron ores have demonstrated that an excess of collector favors flotation of the calcareous gangue materials with the silica and a deficiency favors recovery of the calcareous materials in the iron concentrates. Ability to reject or recover the calcareous materials by control of reagent gives some degree of flexibility to the separation. Economic processing of calcareous iron ores would seem to favor recovery of sufficient lime in the iron concentrates to flux the contained insoluble and yield a self-fluxing product for smelting. Lime in excess of fluxing requirements would reduce the iron content of the beneflcated product and might therefore beobjectionable. Our invention is particularly .well suited for the beneflcation of calcareous iron ores in that it not only permits rejection of siliceous gangue materials, but also enables rejection or recovery of the calcite; limestone, or dolomite in the ores to yield iron enriched concentrates with afavorable lime:silica ratio for smelting.

The above recorded test was about average of a number made on the ore. Tests on substantially deslimed charges of the ore ground in a pebble mill, iron ball mill, or red mill to pass 65, 100, or 200 mesh gave results similar to those records :1. Good flotation of the silica was achieved in all tests by using a moderate quantity of sulfate soap, tallol, sodium oleate, oleic acid, or similar anionic collecting agents in conjunction with sufiicent hydrated lime'to substantially saturate the pulp. 4

of the silica from the iron oxides waseffected by the following reagents expressed in conventional terms of pounds per ton of flotation feed:

Conditioner Rougher Cleaner Reagent No. 1 No. 2

Hydrated Limo Sulfate Soa Time (min. Pulp H Distribution Assay, Percent weight Percent Product Percent Fe Insol. Fe Insol.

Iron Concentrates Rougher Cleaner Composite.

Silica Rejects 6 Composite Feed.... 32. 100. 0 100.

' Soap flotation of the activated silica from the retarded iron oxides rejected 70.4 per cent of the insoluble in the feed with a loss of only 6.2 percent of the iron. The composited iron concentrates from roughing and cleaning represented a recovery of 93.8 percent of the iron in the feed in an enriched product which assayed 5.2.1 percent iron and 13.1 percent insoluble.

A series of flotation tests was made on the ore to determine the influence of various quantities of hydrated lime 0n activation of the silica and retardation of the iron oxides using the grinding, desliming, and flotation procedures previously described. The results of the tests showing the grade and recovery of iron in the composited rougher and cleaner iron concentrates, and the percent of silica (insoluble) rejected by flotation are summarized as follows:

Test No.

H drated ime Composite Iron Concentrates Pulp pH Weight Per cent Per cent Assay Recovery of Fe ns oil Example II A siliceous iron ore was obtained from a weathered outcrop in the Graces Gap area in the Birmingham district, Alabama. The ore was similar to that described in Example I except that atmospheric leaching had substantially removed the calcite leaving a highly siliceous ore, A head analysis of the ore'gave 45.3 percent Fe, 0.5 percent CaO, and 29.6 percent insoluble.

A representative portionof the ore was ground to pass mesh, then deslimed and floated using the procedure described in Example -I. Flotation 76 silica was inferior. Lime in excess of pulp satu- Silica Rejects ration requirements was employed in tests and 6, and was not detrimental.

Example III A sample of crude wash ore was obtained from an operating mine in the Mesabi district, Minnesota. The ore contained hematite as the predominate iron oxide together with specular hematite and magnetite. The gangue was essentially quartz with some iron silicate minerals and clayey material. *A head analysis gave 52.7 percent iron and 20.7 percent insoluble. The ore was crushed to pass 20 mesh and used as feed for flotation testing.

A representative portion of the ore was wetground to pass 100 mesh and deslimed using the procedure previously described in Example I. The granular portion was transferred to a laboratory mechanical flotation cell and diluted with tap water to a pulp consistency of about 20 percent solids. The charge was conditioned with hydrated lime and sulfate soap and floated to remove the bulk of the silica in a roughing operation. A small additional quantity of sulfate soap was added to float the remaining silica in a scavenger operation. The rougher and scavenger froths were combined and triple-cleaned inv the same cell for the final silica rejects. The reagent charge expressed in conventional pounds per, ton of flotation feed was as follows:

Reagent 23 No. 2 No. 3

Hydrated Lime 31.9 Sulfate Soa 1.

Time (min. Pulp pH 12.

Despite the large quantity of hydrated lime employed in the test to substantially saturate the pulp, some of the specular hematite and magnetite floated with the silica. The grade and distribution of iron and silica in the test products are as follows:

Product Pemm Fe Insol. Fe Insol.

Composite Composite Feet...

The results of the recorded test are typical of l0 those obtained on iron ores containing specular hematite or magnetite associated with more earthy varieties of iron oxides. Activation and soap flotation of the siliceous gangue materials in such iron ores will yield acceptable iron concentrates with a moderately good recovery.

While we have disclosed the preferred embodiments of our invention, it will be readily apparent to those skilled in the art that many variations and modifications may be made therein without departing from the spirit of the invention.

What is claimed is:

1. A process for beneficiating iron ores by froth flotation of the siliceous gangue constitutents from iron oxides which comprises adding a suflicient quantity of hydrated lime to a deslimed pulp of the comminuted ore to establish a pulp pH of about 12 and to substantially saturate the pulp with dissolved lime, and an anion-active collecting agent selected from the group consisting of fatty acids, rosin acids, and soaps derived from such acids, and thereafter subjecting said pulp to agitation and aeration whereby siliceous gangue is floated and beneficiated iron ore is depressed and recovered.

2. The process of claim 1, wherein at least about 10.5 pounds of hydrated lime per ton of ore is incorporated in the pulp.

3. The process of claim 1, wherein from 10.5 to 41.8 pounds of hydrated lime per ton of ore is incorporated in the pulp. whereby the presence of an excess of lime insures substantial saturation of the pulp therewith.

4. The process of claim 1, wherein the anionic collecting agent employed is oleic acid.

5. The process of claim 1, wherein-the anionic collecting agent employed is tallol.

6. The process of claim 1, wherein the anionactive collecting agent employed is sulfate soap derived from paper mill black liquor.

JULIUS BRUCE CLEMMER. MILTON FRIEL WILLIAMS, Ja.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,364,777 Brown Dec. 12, 1944 2,387,081 Herkenhofl Oct. 16, 1945 OTHER REFERENCES Keck, A Study of the Flotative Properties of Hematite, A. I. M. ME. Tech. Pub. 763, In Mining Technology 1937, pages 14, 15 and 16.

Gaudln Flotation Fundamental, Part I, 1938. pages 92, 97, 98. 

